1. Field of the Invention
The present invention concerns a ramjet for supersonic and/or hypersonic aircraft designed to operate over a wide range of speeds, for example Mach numbers between 1-2 and 15-20.
2. Description of the Prior Art
French patent application 95 08417 describes a ramjet able to operate over a range of speeds in this order whilst retaining maximum efficiency. To this end, it comprises:
a combustion supporting gas inlet; PA1 a fuel injection device; and PA1 a ramjet body which comprises a combustion chamber in which the combustion supporting gas is mixed with a fuel to be burned and an exhaust nozzle to channel the gases leaving the combustion chamber and which has, at least in a transition area between the combustion chamber and the exhaust nozzle, a variable geometry progressively varying from a convergent then divergent longitudinal section for speeds corresponding to a low Mach number to an approximately constant and then divergent longitudinal section for speeds corresponding to a high Mach number.
A variable geometry of the longitudinal section of the body is obtained, in the embodiment described in the above patent application, by having one of the lateral walls of the body in the form of plates hinged together about axes transverse to the longitudinal direction of the ramjet at least in the transition area (nozzle throat). Accordingly, depending on the selected airspeed, the geometry of the longitudinal section of the body can be varied, in particular in the transition area, by moving the plates progressively into the appropriate position, which enables optimal flight conditions to be conserved for the indicated range of speeds, in particular a maximal thrust value independent of external conditions (fuel consumption, aerodynamic pressure, profile of the flow of combustion supporting gas in the corresponding inlet). In other words, this amounts to "eliminating" the nozzle throat (convergent-divergent geometry) that exists at "low" speeds so as finally to obtain (at a Mach number equal to or greater than around 7) a constant section of the combustion chamber followed by the divergent section of the exhaust nozzle.
Although technically operational, this embodiment of the variable geometry of the body can give rise to problems with correct operation at the hinges of the plates, from the point of view of reliability under extreme conditions, in particular of temperature. Air blower means may then be provided to eliminate these drawbacks. What is more, the set of hinged plates and the blower means, if used, help to increase the mass of the ramjet, which is undesirable.
An object of the present invention is to propose a ramjet in which the design of the variable geometry of the body eliminates the problems referred to hereinabove.